Problem: $\dfrac{9}{2} \div \dfrac{4}{9} = {?}$
Solution: Dividing by a fraction is the same as multiplying by the reciprocal of the fraction. The reciprocal of $\dfrac{4}{9}$ is $\dfrac{9}{4}$ Therefore: $ \dfrac{9}{2} \div \dfrac{4}{9} = \dfrac{9}{2} \times \dfrac{9}{4} $ $ \phantom{\dfrac{9}{2} \times \dfrac{9}{4}} = \dfrac{9 \times 9}{2 \times 4} $ $ \phantom{\dfrac{9}{2} \times \dfrac{9}{4}} = \dfrac{81}{8} $